In this application and merely for clarity purposes, the leading end and edge of sheet material on a roll is considered to be the last quadrant of sheet material exposed on the outside of the roll, i.e. the section 52 of sheet material shown in FIG. 1 from the imaginary line A-A′ to the edge 53. The underlying winding of such a roll is then the piece of sheet material on which the leading edge 52 rests from A-A′ through 360° to A-A′ again.
Joining of the leading edge of one roll or part roll to the trailing edge of a further roll or part roll is typically accomplished by either permanent or flying splicing. The permanent splice should provide a flexible strong connection between the two webs and should maintain substantially all of the properties of the sheet material. For example if the sheet material is paper which can be printed or coated, the permanent splice is preferably thin, flexible, printable, coatable and should also have the same repulpable properties of paper. Flying splices are usually temporary splices made at machine running speed between rolls when it is undesirable to stop the machine, e.g. during coating or printing.
Two common types of splices are known for webs of sheet materials, overlap and butt splices.
For an overlap splice, the leading and trailing edges of the first and second rolls of sheet material are typically joined together by a double-sided adhesive tape as shown in FIG. 2A or B. The double-sided adhesive tape is either a double-coated adhesive tape having a backing member 30 and an adhesive layer 31 and 33 on each side (FIG. 2A) or a transfer tape with a single adhesive layer 31 (FIG. 2B). Such tapes are typically supplied with a single release liner 32. An overlap splice has a disadvantage that there is a considerable step at the change from the first to second sheet material which can disrupt the printing process. Further there is the possibility of the adhesive bleeding out of the splice, which could then adhere layers of sheet material together or damage or obstruct printing machinery.
A typical permanent butt splice is shown in FIG. 3. Here the leading edge of sheet material from one roll 52 and the trailing edge of a further roll 58 are attached to an adhesive layer 11 on a backing 10, and then the splice is covered with a covering adhesive tape 3,4. Such a splice can be made using a splicing tape as shown in FIG. 4 with a single adhesive surface 11 covered with a removable protective film comprising two longitudinal parts 12 and 13 which can be separately removed from the adhesive surface, i.e. a “split release liner”. The butt splice reveals a low profile step, and the possibility of adhesive bleeding is minimal because the butt splice has no exposed adhesive portions. Although the butt splice would be preferred for both and permanent and flying splicing due to above-mentioned advantages, several disadvantages with the application of the tape of the kind shown in FIG. 4 have resulted in this tape not being widely used for permanent or flying splicing. First, the tape must be stretched across the width of a roll, which may be 4 to 10 meters wide with the non-adhesive side of the backing adjacent to the roll. This is usually accomplished by two or more operators, who provisionally place the tape into its final position on the roll using small pieces of adhesive tape. Such a procedure suffers from a number of disadvantages, for example inter alia it is worker-intensive and time-consuming and there is the possibility that the small pieces of tape are inadvertently not removed after application of the tape.
In U.S. Pat. No. 5,212,002, a modified flying butt splice tape is proposed as shown in FIG. 5. The proposed tape consists of a substrate 10, e.g. backing, with an adhesive layer 11 with a split cover liner (12 and 13) on one side and on the opposite at least one narrow adhesive strip 60, 61, 63. After splicing, this splice tape leaves the adhesive strip 60, 61, 63 and thus an exposed surface of adhesive 61 on the underlying winding of the first roll at a distance of approximately one circumference of this roll from the actual splice. This exposed adhesive layer is capable of picking up sheet remnants or attaching itself to other objects or parts of machinery which can disrupt smooth operation, in particular machine printing.
To overcome the above-mentioned disadvantages, WO 94/25380 and WO 95/29115 propose a number of splicing tapes. One general type of proposed tape is shown in FIGS. 6A and B. Said tapes include a splicing portion comprising a backing 10 with an adhesive layer 11 on one side covered with at least one release liner 12, 13 and an attachment portion 21 or 20, 21, which is connected to and distributed along the splicing portion. The attachment portion allows for a releasable and self-supportive attachment of the splicing portion to the outer surface of the underlying winding of the roll of sheet material across the width of the roll. Also, the attachment portion is adapted for releasing at least the splicing portion from the underlying winding of the roll while leaving the outer surface of the underlying winding in a substantially non-tacky condition. The proposed tapes offer a number of advantages. The tape can be placed on the roll of sheet material by a single operator and may be repositionable. Also after splicing substantially no exposed adhesive remains on the outer surface of the underlying wind of the roll.
WO 94/25380 and WO 95/29115 also disclose a method for preparing a splice using the splicing tapes shown in FIGS. 6A and B. In the disclosed method, the splicing tape is attached to the outer surface of the underlying winding using the attachment portion substantially across the width of the roll. The first part of the adhesive layer is exposed by removing the first release liner 12 and then the leading edge is attached to the exposed adhesive layer. The attachment of the leading edge is typically accomplished by pressing the leading edge against the exposed adhesive by hand. Any excess of the leading edge extending over the second release liner of the second part of adhesive layer is folded back, creased and torn off, as is usual in the paper industry, at the transition between first and second release liner. Subsequently, the second part of the adhesive layer is exposed by removing the second release liner 13 manually, which means that the attachment portion comes away from the underlying winding as well as the splicing portion attached to the leading edge. Thereafter, the further end (e.g. the trailing edge) of a second web of sheet material can be fixed in a similar manner on the exposed part of the adhesive layer. Alternatively the roll can be rotated to simplify the application of the further end of second sheet material. For example the further end can be fixed on the exposed adhesive layer as the splicing tape with the exposed adhesive layer rotates through and catches the second sheet material drawn over a guide roller or drum from the web supply. Again any excess of the further end can be subsequently torn off to the correct length in order to form a neat butt splice.
The fixing of the further end of the second web of sheet material to the exposed adhesive layer by hand may be disadvantageous in that it sometimes may be difficult to maintain the proper tension of the roll during said attachment. This is especially true because the tension of the second web is often temporarily released in order to bring further end of said web into position for fixing. The alternative method of rotating the splicing tape with the exposed adhesive layer through to catch the further end of the second web of sheet material can also be disadvantageous, in particular for splicing performed on winders or rewinders having a rider-means. Upon rotation of the roll with the attached splicing tape, the exposed adhesive layer passes over the rider-means. The exposed adhesive layer can pick up dirt, web remnants or the like present on the rider-means.
The term “rider-means” as used above and below is to be understood here as any relatively horizontal means riding on the roll of the web, such as a supporting drum or belt-support or a conventional rider roll. For example, the winder/rewinder available from Valmet Corporation, Helsinki, Finland under the trademark WinDrum L Winder has a supporting drum as a rider-means. Winders/rewinders having a drum as a rider-means are also for example described in U.S. Pat. No. 4,485,979. The winder/rewinders available from Valmet under the trademarks Winbelt Winder, WinRoll Winder and JR 1000 E Winder are examples of winder/rewinders having a belt-support as a rider-means. Winders comprising a belt-support are also for example described in WO 99/55608, U.S. Pat. No. 4,746,076 and U.S. Pat. No. 5,732,902.